The present invention relates to sheet transport apparatus of a printer having a scanner unit in which an upper transport path is provided to extend from a sheet feeding part to an image transfer part arranged over a photosensitive medium.
In general, a printer during operation transports a record sheet from a sheet feeding part to a transfer part through a given transport path, and the transfer part of the printer transfers a visible image formed with toner on a photosensitive medium to the record sheet. The visible image is formed on and carried by the photosensitive medium in accordance with image information. In this type of the printer, the transfer part of the printer is arranged on an upper side of the photosensitive medium, and the sheet feeding part is provided on a lower side of the photosensitive medium. An upper transport path is provided to send a record sheet from the sheet feeding part on a lower side of the printer to the transfer part on an upper side of the printer. This type of the printer is hereinafter referred to as an upper transport type printer.
Conventionally, in order to incorporate a scanner function to the printer, a scanner unit and an image processing unit for processing image readout signals from the scanner unit and sending the signals to the printer are attached to the printer such as the upper transport type printer to constitute an image forming system. In such a conventional image forming system, the printer must be provided with a separate scanner unit and a separate image processing unit. However, there are many inconveniences in using that image forming system to record an image on the sheet, for example, a need of complicated operations, a bulky system size, and a total cost of the printer, the scanner unit and the others becoming unnecessarily high.